Turbocharger

ABSTRACT

A turbocharger includes a turbine housing, an annular metal plate, and a scroll passage defining plate. The metal plate defines a connecting passage in the turbine housing. The connecting passage connects a turbine chamber and a turbine scroll passage to each other. The scroll passage defining plate includes a passage defining portion that defines the turbine scroll passage and an inner circumferential edge portion that extends from the inner circumferential edge portion of the passage defining portion and along the metal plate. The scroll passage defining plate has an inner circumferential edge that is fixed between the turbine housing and the metal plate. The scroll passage defining plate is arranged in the turbine housing such that the outer circumferential edge portion of the passage defining portion is movable relative to the turbine housing.

TECHNICAL FIELD

The present invention relates to a turbocharger.

BACKGROUND ART

A turbocharger includes a bearing housing, a turbine housing, and acompressor housing. The bearing housing rotationally supports animpeller shaft. The turbine housing is coupled to a first end of thebearing housing. Exhaust gas discharged from an internal combustionengine flows inside the turbine housing. The compressor housing iscoupled to a second end of the bearing housing. Intake air conducted tothe internal combustion engine flows inside the compressor housing. Theturbine housing has a turbine chamber. The turbine chamber accommodatesa turbine impeller, which is coupled to a first end of the impellershaft and is rotated integrally with the impeller shaft by exhaust gasdrawn into the turbine chamber. The compressor housing accommodates acompressor impeller, which is coupled to a second end of the impellershaft and is rotated integrally with the impeller. When the turbineimpeller is rotated by exhaust gas discharged from the internalcombustion engine, so that the compressor impeller is rotated integrallywith the turbine impeller through the impeller shaft, the intake airflowing through the compressor housing is compressed by the rotation ofthe compressor impeller, so that the compressed intake air is suppliedto the internal combustion engine. Such forced induction of intake airinto the internal combustion engine performed by the turbochargerincreases the intake efficiency of the internal combustion engine,thereby improving the performance of the internal combustion engine.

The turbocharger includes a catalyst that purifies exhaust gas on thedownstream side of the turbine housing in the flowing direction of theexhaust gas. When heated to a temperature higher than or equal to theactivation temperature, the catalyst exerts exhaust gas purifyingcapability. Thus, for example, when the exhaust gas temperature is low,the catalyst is not heated to a temperature higher than or equal to theactivation temperature, so that the catalyst may not sufficiently purifythe exhaust gas.

Typically, since a turbine housing needs to have a sufficient stiffness,the turbine housing is formed through casting to have thick walls.Accordingly, the turbine housing has a large mass and a large heatcapacity. Thus, the heat of the exhaust gas flowing through the turbinehousing is removed, so that the temperature is reduced. This extends thetime for the catalyst to reach the activation temperature. Therefore,under the operating condition in which there is a demand for earlywarm-up of the catalyst, for example, during cold start of the internalcombustion engine, the catalyst cannot be heated to a temperature higherthan or equal to the activation temperature at an early stage.

As such, the turbocharger of Patent Document 1 includes a turbine scrollpassage that is a part of the passage for conducting exhaust gas thathas flowed into the turbine housing to the turbine housing. A part ofthe wall surface of the turbine scroll passage is constituted by ascroll passage defining plate (a heat shield plate). The scroll passagedefining plate limits the transfer of heat from the exhaust gas to theturbine housing. This limits the reduction in the temperature of theexhaust gas while the exhaust gas flows through the turbine housing.

The turbocharger of Patent Document 1 also includes nozzle vanes (avariable valve). The nozzle vanes are pivotally supported by a firstplate and a second plate, which are arranged to be opposed to eachother. The first plate and the second plate define a connecting passagethat connects the turbine scroll passage and the turbine chamber to eachother in the turbine housing. The nozzle vanes are capable of changingthe flow passage area of the connecting passage and regulates the flowvelocity of the exhaust gas conducted to the turbine chamber.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent No. 5880463

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

In Patent Document 1, one of the peripheral portions of the scrollpassage defining plate is fixed by being held between the turbinehousing and the bearing housing, and the other edge portion is fixed bybeing held between the turbine housing and the second plate. Thisconfiguration does not readily allow for thermal expansion of the scrollpassage defining plate when the scroll passage defining plate is warmedup by exhaust gas. The scroll passage defining plate thus may receive anexcessive stress locally.

Accordingly, it is an objective of the present invention to provide aturbocharger that allows for thermal expansion of a scroll passagedefining plate.

Means for Solving the Problems

To achieve the foregoing objective, a turbocharger is provided thatincludes a bearing housing, a turbine housing, a turbine chamber, aturbine impeller, a turbine scroll passage, a connecting passage, anannular metal plate, and a scroll passage defining plate. The bearinghousing rotationally supports an impeller shaft. The turbine housing isa cast component coupled to an end of the bearing housing in a rotationaxis direction of the impeller shaft. Exhaust gas discharged from aninternal combustion engine flows inside the turbine housing. The turbinechamber is defined in the turbine housing. The turbine impeller isaccommodated in the turbine chamber and is configured to be rotatedintegrally with the impeller shaft by exhaust gas drawn into the turbinechamber. The turbine scroll passage is defined in the turbine housingand is a part of a passage for conducting exhaust gas that has flowedinto the turbine housing to the turbine chamber. The turbine scrollpassage surrounds a circumference of the turbine chamber. The connectingpassage is defined in the turbine housing and connects the turbinescroll passage and the turbine chamber to each other. The annular metalplate constitutes a part of a wall surface of the connecting passage.The scroll passage defining plate includes a passage defining portionand an inner circumferential edge. The passage defining portion isarranged such that a predetermined clearance is provided between thepassage defining portion and the turbine housing. The passage definingportion constitutes a part of a wall surface of the turbine scrollpassage. The inner circumferential edge extends from an innercircumferential edge portion of the passage defining portion and alongthe metal plate. The scroll passage defining plate is arranged in theturbine housing such that: the inner circumferential edge is fixedbetween the turbine housing and the metal plate; and an outercircumferential edge portion of the passage defining portion that is ona side opposite from the inner circumferential edge portion is movablerelative to the turbine housing.

The outer circumferential edge portion of the scroll passage definingplate, which is on the opposite side from the inner circumferential edgeportion in the passage defining portion, is movable relative to theturbine housing. This configuration allows for thermal expansion of thescroll passage defining plate when the scroll passage defining plate iswarmed up by exhaust gas.

In the above-described turbocharger, the scroll passage defining platemay be arranged in the turbine housing such that the outercircumferential edge portion of the passage defining portion and aninner circumferential surface of the turbine housing are spaced apartfrom each other.

The outer circumferential edge portion of the passage defining portionand the inner circumferential surface of the turbine housing are spacedapart from each other. This configuration allows for thermal expansionof the scroll passage defining plate when the scroll passage definingplate is warmed up by exhaust gas.

The above-described turbocharger may further include an elastic memberconfigured to provide a clearance between the passage defining portionof the scroll passage defining plate and the turbine housing.

If the elastic member is arranged between the outer circumferential endand the turbine housing, elastic deformation of the elastic memberallows for thermal expansion of the scroll passage defining plate whenthe scroll passage defining plate is warmed up by exhaust gas.

In the above-described the turbocharger, the elastic member may bearranged between the outer circumferential edge portion of the passagedefining portion and the turbine housing, and the outer circumferentialedge portion of the passage defining portion may be supported by theturbine housing with the elastic member in between.

The outer circumferential edge portion of the passage defining portionof the scroll passage defining plate is supported by the turbine housingwith the scroll elastic member. This configuration suppresses vibrationsof the scroll passage defining plate.

The above-described turbocharger according may further include anannular leaf spring that is arranged between the inner circumferentialedge of the scroll passage defining plate and the turbine housing. Thescroll passage defining plate may be fixed by holding the innercircumferential edge between the leaf spring and the metal plate.

If the scroll passage defining plate is fixed to the turbine housing byholding the inner circumferential edge of the scroll passage definingplate between the leaf spring and the metal plate, the contact areabetween the turbine housing and the scroll passage defining plate isreduced. This limits the transfer of heat from the exhaust gas flowingthrough the turbine scroll passage to the turbine housing.

In the above-described turbocharger, the scroll passage defining platemay be fixed by holding the inner circumferential edge between theturbine housing and the metal plate.

Since the inner circumferential edge of the scroll passage definingplate is held between the turbine housing and the metal plate, the innercircumferential edge of the scroll passage defining plate is fixed tothe turbine housing.

In the above-described turbocharger, the scroll passage defining platemay include an outer circumferential wall that constitutes an outercircumferential interior surface of the turbine scroll passage, an innercircumferential wall that is located inward from the outercircumferential wall in a radial direction of the impeller shaft andconstitute an inner circumferential interior surface of the turbinescroll passage, and a linking wall that links the outer circumferentialwall and the inner circumferential wall to each other. The innercircumferential edge of the scroll passage defining plate may extendfrom the inner circumferential wall and inward in the radial directionof the impeller shaft.

If the scroll passage defining plate includes the linking wall and theinner circumferential edge in addition to the inner circumferential walland the outer circumferential wall, the scroll passage defining platehas a sufficient stiffness.

In the above-described turbocharger, a heat insulator may be arranged inthe clearance between the passage defining portion of the scroll passagedefining plate and the turbine housing.

If the heat insulator is arranged in the clearance between the passagedefining portion of the scroll passage defining plate and the turbinehousing, the transfer of heat from the exhaust gas flowing through theturbine scroll passage to the turbine housing is limited.

The above-described turbocharger further includes a plurality of nozzlevanes that is arranged in the connecting passage and causes exhaust gasin the turbine scroll passage to flow to the turbine chamber. The metalplate may support the nozzle vanes.

If the metal plate supports the nozzle vanes, the same member can beused as the member that supports the inner circumferential edge of thescroll passage defining plate and the member that supports the nozzlevanes.

In the above-described turbocharger, the nozzle vanes may be movablevanes that are pivotally supported by the metal plate so as to becapable of changing a flow passage area of the connecting passage. Theturbocharger may further include a metal support plate. The supportplate may cooperate with the metal plate to pivotally support the nozzlevanes and is arranged to be opposed to the metal plate so as toconstitute a part of the wall surface of the connecting passage.

If the metal support plate, which supports the nozzle vanes, is arrangedto be opposed to the metal plate, the connecting passage is providedbetween the support plate and the metal plate. Further, the movablevanes are capable of changing the flow passage area of the connectingpassage.

The above-described turbocharger may further include a metal annularplate. The annular plate may be arranged to be opposed to the scrollpassage defining plate so as to constitute a part of the wall surface ofthe turbine scroll passage. An outer circumferential edge of the annularplate may be held between the turbine housing and the bearing housing.

A part of the wall surface of the turbine scroll passage is made of themetal annular plate. This limits the transfer of heat from the exhaustgas flowing through the turbine scroll passage to the turbine housing.

The above-described turbocharger may further include a metal annularplate. The annular plate may be arranged to be opposed to the scrollpassage defining plate so as to constitute a part of the wall surface ofthe turbine scroll passage. A thickness of the annular plate may besmaller than a thickness of the support plate and a thickness of themetal plate. An outer circumferential edge of the annular plate may beheld between the turbine housing and the bearing housing.

If the annular plate, which is thinner and has a smaller heat capacitythan the support plate and the metal plate, constitutes the wall surfaceof the turbine scroll passage, the reduction in the temperature of theexhaust gas flowing through the turbine scroll passage is limited.

In the above-described the turbocharger, the annular plate may includean annular rib. The rib may protrude from an inner circumferentialportion of the annular plate in the rotation axis direction of theimpeller shaft and extends away from the scroll passage defining plate.

When the annular plate includes an annular rib, the annular plate has asufficient stiffness as compared to a case in which the annular platedoes not have a rib. Also, vibrations in a section close to the innercircumferential portion of the annular plate are suppressed as comparedto a case in which the annular plate does not have the rib.

In the above-described turbocharger, the scroll passage defining platemay include a flange portion that extends from the outer circumferentialedge portion of the passage defining portion and outward in the radialdirection of the impeller shaft. A clearance may be provided between theflange portion and the annular plate. The flange portion may extendalong the annular plate.

If the clearance is provided between the flange portion of the scrollpassage defining plate and the annular plate, thermal expansion of thescroll passage defining plate is permitted.

In the above-described turbocharger, the flange portion may extendoutward in the radial direction of the impeller shaft such that aclearance is provided between the flange portion of the scroll passagedefining plate and the inner circumferential surface of the turbinehousing.

If the clearance is provided between the flange portion and the innercircumferential surface of the turbine housing, the space providedbetween the passage defining portion of the scroll passage definingplate and the inner circumferential surface of the turbine housing isconnected to the interior of the turbine scroll passage. This isunlikely to cause a pressure difference between the interior of theturbine scroll passage and the space provided between the passagedefining portion of the scroll passage defining plate and the innercircumferential surface of the turbine housing. This limits deformationof the scroll passage defining plate caused by the pressure difference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a turbocharger according to anembodiment.

FIG. 2 is an enlarged cross-sectional side view illustrating a part ofthe turbocharger of FIG. 1.

FIG. 3 is a vertical cross-sectional view illustrating the turbochargerof FIG. 1.

FIG. 4 is an enlarged cross-sectional side view illustrating a part of aturbocharger according to a first modification.

FIG. 5 is an enlarged cross-sectional side view illustrating a part of aturbocharger according to a second modification.

FIG. 6 is a cross-sectional view of the annular plate of theturbocharger of FIG. 1.

FIG. 7 is a cross-sectional view illustrating a modification of theannular plate of FIG. 6.

FIG. 8 is a cross-sectional view illustrating a partial modification ofthe turbocharger of FIG. 3.

MODES FOR CARRYING OUT THE INVENTION

A turbocharger according to one embodiment will now be described withreference to FIGS. 1 to 3.

As shown in FIG. 1, a turbocharger 10 includes a case 11 that includes abearing housing 20, a turbine housing 30, and a compressor housing 40.The bearing housing 20, the turbine housing 30, and the compressorhousing 40 are cast components. Exhaust gas discharged from an internalcombustion engine E flows through the turbine housing 30. Intake air tobe drawn into the internal combustion engine E flows through thecompressor housing 40.

The bearing housing 20 rotationally supports an impeller shaft 12. Aturbine impeller 13 is coupled to a first end of the impeller shaft 12in the rotation axis direction. A compressor impeller 14 is coupled to asecond of the impeller shaft 12 in the rotation axis direction. Theturbine housing 30 is coupled to a first of the bearing housing 20 inthe rotation axis direction of the impeller shaft 12. The compressorhousing 40 is coupled to a second of the bearing housing 20 in therotation axis direction of the impeller shaft 12.

The bearing housing 20 includes a tubular main body 21. The main body 21has an insertion hole 21 h, through which the impeller shaft 12 isinserted. The main body 21 rotationally supports the impeller shaft 12,which is inserted through the insertion hole 21 h, with radial bearings15. The axial direction of the main body 21 matches the rotation axisdirection of the impeller shaft 12.

The main body 21 has a first end face 21 a, which is located at a firstend in the rotation axis direction of the impeller shaft 12, and asecond end face 21 b, which is located at a second end in the rotationaxis direction of the impeller shaft 12. The main body 21 has an annularprotrusion 21 f, which protrudes from the first end face 21 a. Theprotrusion 21 f has a flat end face 21 e at the distal end. The end face21 e extends in the radial direction of the impeller shaft 12. A firstend of the insertion hole 21 h opens in the end face 21 e of theprotrusion 21 f. An annular protuberance 21 g is provided on the endface 21 e of the protrusion 21 f. The protuberance 21 g projects fromthe end face 21 e so as to surround the opening of the insertion hole 21h.

The main body 21 has a columnar accommodation recess 21 c provided inthe second end face 21 b. A second end of the insertion hole 21 h opensin the bottom surface of the accommodation recess 21 c. The diameter ofthe accommodation recess 21 c is larger than the diameter of theinsertion hole 21 h. The axis of the accommodation recess 21 c matchesthe axis of the insertion hole 21 h. The accommodation recess 21 caccommodates a thrust bearing 16. The thrust bearing 16 is accommodatedin the accommodation recess 21 c while contacting the bottom surface ofthe accommodation recess 21 c.

The bearing housing 20 includes a first flange portion 22 and a secondflange portion 23. The first flange portion 22 protrudes outward in theradial direction of the impeller shaft 12 from the first end in theaxial direction of the main body 21 on the outer circumferential surfaceof the main body 21. The second flange portion 23 protrudes outward inthe radial direction of the impeller shaft 12 from the second end in theaxial direction of the main body 21 on the outer circumferential surfaceof the main body 21. The second flange portion 23 is annular.

The first flange portion 22 has an annular first extended portion 24, acylindrical second extended portion 25, and an annular third extendedportion 26. The first extended portion 24 extends outward in the radialdirection of the impeller shaft 12 from the outer circumferentialsurface of the main body 21. The second extended portion 25 extends awayfrom the second flange portion 23 in the rotation axis direction of theimpeller shaft 12 from the distal end of the first extended portion 24.The third extended portion 26 extends outward in the radial direction ofthe impeller shaft 12 from a section that is slightly closer to thefirst extended portion 24 in the rotation axis direction than an endface 25 a of the second extended portion 25.

The first extended portion 24 has an end face 24 a that is on theopposite side from the second flange portion 23 and is continuous withthe first end face 21 a of the main body 21. The third extended portion26 has an end face 26 a located on the opposite side from the firstextended portion 24. The end face 25 a of the second extended portion 25is farther from the first extended portion 24 than the end face 26 a ofthe third extended portion 26. The end face 25 a of the second extendedportion 25 is a flat surface that extends in the radial direction of theimpeller shaft 12.

The compressor housing 40 has a compressor main body 41. The compressormain body 41 has a substantially disk-shaped end wall 41 a and anannular circumferential wall 41 b, which extends in the rotation axisdirection of the impeller shaft 12 from the circumferential edge of theend wall 41 a. The end of the circumferential wall 41 b on the oppositeside from the end wall 41 a is open. The compressor housing 40 iscoupled to the second end of the bearing housing 20 by attaching thesecond flange portion 23 to the open end of the circumferential wall 41b with bolts (not shown). The opening of the circumferential wall 41 bis closed by the second end face 21 b of the main body 21 and the endface of the second flange portion 23 on the opposite side from the firstflange portion 22. That is, the opening of the circumferential wall 41 bis closed by the end face located at the second end of the bearinghousing 20.

The compressor housing 40 further has a compressor tubular portion 42,which protrudes from the end wall 41 a. The compressor tubular portion42 extends away from the circumferential wall 41 b. The compressortubular portion 42 has an intake port 42 a. The intake port 42 a extendsin the rotation axis direction of the impeller shaft 12. The axis of theintake port 42 a matches the rotation axis of the impeller shaft 12.

The compressor housing 40 has a compressor impeller chamber 43, adiffuser passage 44, and a compressor scroll passage 45. The compressorimpeller chamber 43 is connected to the intake port 42 a andaccommodates the compressor impeller 14. The compressor scroll passage45 spirals around the outer circumference of the compressor impellerchamber 43. The diffuser passage 44 extends annularly about thecompressor impeller chamber 43 and connects the compressor impellerchamber 43 and the compressor scroll passage 45 to each other.

An annular shroud member 46 is provided in the compressor housing 40.The shroud member 46 includes a cylindrical portion 46 a, which extendsin the axial direction along the inner circumferential surface of thecompressor tubular portion 42, and an annular portion 46 b, whichextends from an end in the axial direction of the cylindrical portion 46a along the end wall 41 a. The compressor impeller chamber 43 is a spacesurrounded by the cylindrical portion 46 a of the shroud member 46 andthe accommodation recess 21 c of the bearing housing 20.

The compressor impeller 14 has a shaft insertion hole 14 h, whichextends in the rotation axis direction of the impeller shaft 12. Theimpeller shaft 12 can be passed through the shaft insertion hole 14 h.The second end in the rotation axis direction of the impeller shaft 12projects into the compressor impeller chamber 43. The compressorimpeller 14 is attached to the impeller shaft 12, for example, with anut, while the part of the impeller shaft 12 projecting into thecompressor impeller chamber 43 is inserted through the shaft insertionhole 14 h, such that the compressor impeller 14 is integrally rotationalwith the impeller shaft 12. The end of the compressor impeller 14 thatis closer to the bearing housing 20 is supported by the thrust bearing16 with a sealing collar or a thrust collar (neither is shown) inbetween. The thrust bearing 16 receives the load that acts on thecompressor impeller 14 in the thrust direction (axial direction).

The annular portion 46 b of the shroud member 46 includes a flat surface46 c, which is opposed to the bearing housing 20. The flat surface 46 cextends in the radial direction of the impeller shaft 12. The diffuserpassage 44 is provided between the flat surface 46 c of the annularportion 46 b and the second end face 21 b of the bearing housing 20,which is opposed to the flat surface 46 c in the rotation axis directionof the impeller shaft 12.

An annular scroll member 47 is provided in the compressor housing 40.The scroll member 47 extends about the shroud member 46. The compressorscroll passage 45 is defined by the outer circumferential surface of theannular portion 46 b of the shroud member 46, the end wall 41 a of thecompressor main body 41, and the inner circumferential surface of theshroud member 46. The scroll member 47 and the shroud member 46 do notnecessarily need to be components separate from the compressor housing40, but may be integrated with the compressor housing 40.

As shown in FIG. 2, the turbine housing 30 has a turbine main body 31.The turbine main body 31 has a substantially disk-shaped end wall 31 aand an annular circumferential wall 31 b, which is located radiallyoutward from the end wall 31 a and extends in the rotation axisdirection of the impeller shaft 12. The end of the circumferential wall31 b on the opposite side from the end wall 31 a is open.

The open end of the circumferential wall 31 b includes an end face 31 dand an annular flange 31 f, which protrudes outward in the radialdirection of the impeller shaft 12. The flange 31 f has an end face 31 con the opposite side from the end wall 31 a in the axial direction. Theend face 31 c protrudes further in the axial direction than the end face31 d of the circumferential wall 31 b. The end face 31 c of the flange31 f and the end face 31 d of the circumferential wall 31 b are flatsurfaces extending in the radial direction of the impeller shaft 12.

The flange 31 f is attached to the third extended portion 26 of thebearing housing 20 by fasteners (for example, bolts 17) with the endface 31 c of the flange 31 f and the end face 26 a of the third extendedportion 26 brought into contact with each other, so that the turbinehousing 30 is coupled to the first end of the bearing housing 20.

A seal member 18 is provided between the flange 31 f and the thirdextended portion 26 of the bearing housing 20. The seal member 18 sealsthe interface between the end face 31 c of the flange 31 f and the endface 26 a of the third extended portion 26.

The turbine housing 30 has a turbine tubular portion 32, which protrudesfrom the end wall 31 a. The turbine tubular portion 32 extends away fromthe circumferential wall 31 b. The turbine tubular portion 32 has adischarge port 32 a. The discharge 32 a extends in the rotation axisdirection of the impeller shaft 12. The axis of the discharge port 32 amatches the rotation axis of the impeller shaft 12. The turbine tubularportion 32 has, at the open end, a flat open end face 32 e, whichextends in the radial direction of the impeller shaft 12.

The turbine tubular portion 32 has, at the open end, an annular couplingflange 32 f. A downstream exhaust pipe 19, which has a coupling flange19 f and an end face 19 e at the open end, is connected to the dischargeport 32 a. The downstream exhaust pipe 19 is coupled to the turbinetubular portion 32 with the coupling flange 19 f and the coupling flange32 f of the turbine tubular portion 32 being clamped by a clamp member19 c. The end face 19 e of the downstream exhaust pipe 19 is a flatsurface that extends in parallel with the open end face 32 e of theturbine tubular portion 32.

The downstream exhaust pipe 19 connects the turbocharger 10 to acatalyst C1, which is provided on the downstream side of the turbinehousing 30 in the flowing direction of exhaust gas. The catalyst C1purifies exhaust gas. When heated to a temperature higher than or equalto the activation temperature, the catalyst C1 exerts exhaust gaspurifying capability.

The turbine housing 30 has a turbine chamber 33, a connecting passage34, and a turbine scroll passage 35. The turbine impeller 13 isaccommodated in the turbine chamber 33. The turbine scroll passage 35spirals around the turbine chamber 33. The turbine scroll passage 35thus surrounds the circumference of the turbine chamber 33. The turbinescroll passage 35 is a part of the passage that conducts exhaust gasthat has flowed into the turbine housing 30 to the turbine chamber 33.The connecting passage 34 extends annularly about the turbine chamber 33and connects the turbine scroll passage 35 and the turbine chamber 33 toeach other.

The turbocharger 10 includes nozzle vanes 50, a first plate 51, and asecond plate 52. The nozzle vanes 50 are movable vanes that are capableof changing the flow passage area of the connecting passage 34 andregulates the flow velocity of the exhaust gas conducted to the turbinechamber 33. The nozzle vanes 50 are arranged at intervals in thecircumferential direction of the connecting passage 34.

The first plate 51 extends annularly about the protrusion 21 f of thebearing housing 20. The first plate 51 is an annular metal support platethat pivotally supports the nozzle vanes 50 and constitutes the wallsurface of the connecting passage 34 that is closer to the bearinghousing 20. The first plate 51 includes an annular protuberance 51 f,which projects inward in the radial direction of the impeller shaft 12from the inner circumferential surface of the first plate 51. Theprotuberance 51 f is opposed to the protrusion 21 f in the rotation axisdirection of the impeller shaft 12.

The second plate 52 includes a cylindrical portion 52 a, which extendsin the axial direction along the inner circumferential surface of theturbine tubular portion 32, and an annular portion 52 b, which iscontinuous with the cylindrical portion 52 a and extends radiallyoutward from the cylindrical portion 52 a along an inner surface 31 e ofthe end wall 31 a. The turbine chamber 33 is a space surrounded by thecylindrical portion 52 a of the second plate 52, the protuberance 51 fof the first plate 51, and the end face 21 e of the protrusion 21 f ofthe bearing housing 20. That is, the second plate 52 is arranged in theturbine housing 30 to constitute a part of the turbine housing 30. Theturbine chamber 33 is connected to the discharge port 32 a. The exhaustgas that has passed through the turbine chamber 33 is conducted to thedischarge port 32 a.

The annular portion 52 b of the second plate 52 is arranged to beopposed to the first plate 51 in the rotation axis direction of theimpeller shaft 12. The second plate 52 is an annular metal plate thatcooperates with the first plate 51 to pivotally support the nozzle vanes50. The annular portion 52 b constitutes a wall surface of theconnecting passage 34 on the opposite side from the bearing housing 20.The distance between the first plate 51 and the second plate 52 in therotation axis direction of the impeller shaft 12 is maintained bypillar-shaped spacers 53. The spacers 53 are arranged at intervals inthe circumferential direction of the connecting passage 34.

In the rotation axis direction of the impeller shaft 12, a link member54 for driving the nozzle vanes 50, is arranged between the first plate51 and the bearing housing 20. The space between the first plate 51 andthe bearing housing 20 is a heat insulating air layer.

The turbine impeller 13 has a fitting protuberance 13 f, which protrudestoward the insertion hole 21 h. The impeller shaft 12 has a fittingrecess 12 f at a first end in the rotation axis direction. The fittingprotuberance 13 f can be fitted to the fitting recess 12 f. The turbineimpeller 13 is attached to the impeller shaft 12, for example, bywelding, with the fitting protuberance 13 f fitted to the fitting recess12 f of the impeller shaft 12. This allows the turbine impeller 13 torotate integrally with the impeller shaft 12. The turbine impeller 13 isrotated by exhaust gas drawn into the turbine chamber 33. As the turbineimpeller 13 rotates, the impeller shaft 12 rotates integrally.

An annular leaf spring 55 is attached to the protuberance 21 g of theprotrusion 21 f. The outer circumferential edge of the leaf spring 55 isin contact with the end face of the protuberance 51 f of the first plate51 that faces the bearing housing 20. The leaf spring 55 urges the firstplate 51 away from the bearing housing 20. Accordingly, the first plate51, the spacers 53, and the second plate 52 are supported by the endwall 31 a while being pressed against the end wall 31 a of the turbinemain body 31.

The turbine housing 30 has a bulging wall 36, which is located in theouter circumferential portion of the end wall 31 a of the turbine mainbody 31 and bulges away from the bearing housing 20. The bulging wall 36surrounds the circumference of the turbine tubular portion 32. Thebulging wall 36 includes a bulging outer circumferential wall 36 a, abulging inner circumferential wall 36 b, and a bulging linking wall 36c. The bulging outer circumferential wall 36 a is continuous with theend of the circumferential wall 31 b of the turbine main body 31 on theopposite side from the open end and extends in the rotation axisdirection of the impeller shaft 12. The bulging inner circumferentialwall 36 b is located radially inward from the bulging outercircumferential wall 36 a and is continuous with the part of the endwall 31 a that is radially inward from the impeller shaft 12 withrespect to the bulging wall 36. The bulging linking wall 36 c is curvedto be arcuate so as to project away from the bearing housing 20. Thebulging linking wall 36 c links the edge of the bulging outercircumferential wall 36 a on the side opposite from the bearing housing20 to the edge of the bulging inner circumferential wall 36 b on theside opposite from the bearing housing 20.

The turbocharger 10 includes a scroll passage defining plate 60, whichis made of a metal plate that constitutes a part of the wall surface ofthe turbine scroll passage 35. The scroll passage defining plate 60 ismade of a metal sheet, that is, formed through sheet-metal working, andis not formed through casting. The thickness of the scroll passagedefining plate 60 is less than the thicknesses of the first plate 51 andthe second plate 52. The scroll passage defining plate 60 spirals aroundthe turbine chamber 33. The scroll passage defining plate 60 includes anouter circumferential wall 61, an inner circumferential wall 62, alinking wall 63, and an inner circumferential edge 64.

The outer circumferential wall 61, the inner circumferential wall 62,and the linking wall 63 function as a passage defining portion. Thepassage defining portion is arranged to have a predetermined clearancefrom the turbine housing 30 and constitutes a part of the wall surfaceof the turbine scroll passage 35. A predetermined region in the innercircumferential wall 62 that includes the end continuous with the innercircumferential edge 64 is the inner circumferential edge portion of thepassage defining portion. The outer circumferential wall 61 and theinner circumferential wall 62 extend in the rotation axis direction ofthe impeller shaft 12. The scroll passage defining plate 60 thus has asufficient stiffness if the scroll passage defining plate 60 includesthe linking wall 63 and the inner circumferential edge 64 in addition tothe inner circumferential wall 62 and the outer circumferential wall 61,and the linking wall 63 and the inner circumferential edge 64 extend indirections different from those of the inner circumferential wall 62 andthe outer circumferential wall 61.

The outer circumferential wall 61 is located inward from the secondplate 52 in the radial direction of the impeller shaft 12 to surroundthe turbine chamber 33 and constitute an outer circumferential interiorsurface 35 a of the turbine scroll passage 35. The outer circumferentialwall 61 extends along the inner circumferential surface of thecircumferential wall 31 b of the turbine main body 31 and the innercircumferential surface of the bulging outer circumferential wall 36 a.The outer circumferential surface 61 a of the outer circumferential wall61 is spaced apart from the inner circumferential surface of the innercircumferential surface of the circumferential wall 31 b and the innercircumferential surface of the bulging outer circumferential wall 36 a.

The inner circumferential wall 62 is located radially inward from theouter circumferential wall 61 and constitutes an inner circumferentialinterior surface 35 b of the turbine scroll passage 35. The innercircumferential wall 62 extends along the inner circumferential surfaceof the bulging inner circumferential wall 36 b. An outer circumferentialsurface 62 a of the inner circumferential wall 62 is spaced apart fromthe inner circumferential surface of the bulging inner circumferentialwall 36 b. The inner circumferential surface of the innercircumferential wall 62 constitutes the inner circumferential interiorsurface 35 b of the turbine scroll passage 35. The inner circumferentialsurface of the inner circumferential wall 62 is located at the sameposition in the radial direction of the impeller shaft 12 as the outercircumferential edge of the annular portion 52 b of the second plate 52.The outer circumferential edge of the annular portion 52 b of the secondplate 52 may protrude further outward in the radial direction of theimpeller shaft 12 than the inner circumferential surface of the innercircumferential wall 62 or may be located inward from the innercircumferential surface of the inner circumferential wall 62 in theradial direction of the impeller shaft 12.

The linking wall 63 links the edge of the outer circumferential wall 61on the side opposite from the bearing housing 20 to the edge of theinner circumferential wall 62 on the side opposite from the bearinghousing 20. The linking wall 63 extends along the inner circumferentialsurface of the bulging linking wall 36 c and is curved to be arcuate soas to project away from the bearing housing 20. An outer circumferentialsurface 63 a of the linking wall 63 is spaced apart from the innercircumferential surface of the bulging linking wall 36 c.

The inner circumferential edge 64 extends inward in the radial directionof the impeller shaft 12 from the edge of the inner circumferential wall62 that is closer to the bearing housing 20. The inner circumferentialedge 64 is located, in the rotation axis direction of the impeller shaft12, between the end wall 31 a of the turbine main body 31 and theannular portion 52 b of the second plate 52, and extends along theannular portion 52 b. The inner circumferential edge 64 is held betweenthe end wall 31 a and the annular portion 52 b by the urging force ofthe leaf spring 55. That is, the inner circumferential edge 64 of thescroll passage defining plate 60 is fixed by being held between theturbine housing 30 and the second plate 52. In this manner, the metalplate 52 is used as both of a member that supports the nozzle vanes 50and a member that holds the inner circumferential edge 64 of the scrollpassage defining plate 60.

The turbocharger 10 includes a scroll heat insulator 65. The scroll heatinsulator 65 is made of a ceramic material such as alumina and silicafiber. The scroll heat insulator 65 extends over the space between theouter circumferential surface 61 a of the outer circumferential wall 61and the inner circumferential surface of the circumferential wall 31 b,the space between the outer circumferential surface 61 a of the outercircumferential wall 61 and the inner circumferential surface of thebulging outer circumferential wall 36 a, the space between the outercircumferential surface 63 a of the linking wall 63, and the spacebetween the outer circumferential surface 62 a of the innercircumferential wall 62 and the inner circumferential surface of thebulging inner circumferential wall 36 b. The scroll heat insulator 65 isa scroll heat insulating layer that is arranged in a clearance betweenthe passage defining portion of the scroll passage defining plate 60 andthe turbine housing 30.

The heat insulating layer provided between the passage defining portionof the scroll passage defining plate 60 (the outer circumferential wall61, the linking wall 63, and the inner circumferential wall 62) and theturbine housing 30 may be an air layer. To provide an air layer, theouter circumferential wall 61, the linking wall 63, and the innercircumferential wall 62 may be spaced apart from the turbine housing 30without providing the scroll heat insulator 65. If the contact areabetween the scroll passage defining plate 60 and the turbine housing 30is reduced in this manner, the transfer of heat to the turbine housing30 is limited. Also, the air layer provided inward from the turbinehousing 30 functions as space that allows for thermal expansion of thescroll passage defining plate 60.

A scroll elastic member 66 is arranged between the turbine housing 30and the end of the outer circumferential surface 61 a of the outercircumferential wall 61 that is on the opposite side from the linkingwall 63. In other words, the scroll elastic member 66 is arranged toprovide a clearance between the outer circumferential wall 61 (thepassage defining portion of the scroll passage defining plate 60) andthe turbine housing 30. The scroll elastic member 66 is located closerto the bearing housing 20 than the scroll heat insulator 65. The scrollelastic member 66 is, for example, an annular wire mesh attached to theouter circumferential surface 61 a of the outer circumferential wall 61.The scroll elastic member 66 is provided in a crushed state between theouter circumferential surface 61 a of the outer circumferential wall 61and the circumferential wall 31 b of the turbine main body 31.

The scroll elastic member 66 is welded to the outer circumferentialsurface 61 a of the outer circumferential wall 61, for example, by microspot welding. The outer circumferential wall 61 is thus supported by theturbine housing 30 with the scroll elastic member 66 in between.

The scroll passage defining plate 60 includes an annular flange portion67, which extends outward in the radial direction of the impeller shaft12 from the edge of the outer circumferential wall 61 on the sideopposite from the linking wall 63. A predetermined region in the outercircumferential wall 61 that includes the end continuous with the flangeportion 67 is the outer circumferential edge portion of the passagedefining portion. The flange portion 67 extends toward the innercircumferential surface of the circumferential wall 31 b of the turbinemain body 31 such that a clearance is provided between the flangeportion 67 and the inner circumferential surface of the turbine housing30. Since a clearance is provided between the distal end of the flangeportion 67 and the circumferential wall 31 b, the flange portion 67 doesnot contact the circumferential wall 31 b.

The turbocharger 10 includes an annular plate 70 made of a metal sheet.The annular plate 70 constitutes a wall surface of the turbine scrollpassage 35 that is closer to the bearing housing 20. The annular plate70 is located radially outward from the turbine impeller 13 in theradial direction of the impeller shaft 12. The annular plate 70 isarranged about the first plate 51. In the rotation axis direction of theimpeller shaft 12, the annular plate 70 is arranged to be opposed to thescroll passage defining plate 60, particularly, most of the linking wall63. The thickness of the annular plate 70 is smaller than thethicknesses of the first plate 51 and the second plate 52.

A heat insulating layer may be provided between the set of the annularplate 70 and the support plate 51 and the set of the end face 24 a ofthe bearing housing 20 and the first end face 21 a. The heat insulatinglayer is, for example, an air layer. Specifically, a space forinsulating heat may be provided between the set of the innercircumferential portion of the annular plate 70 and the support plate 51and the set of the end face 24 a of the bearing housing 20 and the firstend face 21 a. The heat insulating layer limits the transfer of heatfrom exhaust gas flowing through the turbine scroll passage 35 and theconnecting passage 34 to the bearing housing 20.

The flange portion 67 of the scroll passage defining plate 60 extendsalong the annular plate 70. A clearance may be provided between theflange portion 67 and the annular plate 70. The clearance between theflange portion 67 and the annular plate 70 allows for thermal expansionof the scroll passage defining plate 60.

The turbine scroll passage 35 is provided by the scroll passage definingplate 60, the annular plate 70, the outer circumferential edge of theannular portion 52 b of the second plate 52, and the outercircumferential portion of the first plate 51. The outer circumferentialportion of the first plate 51 protrudes further outward in the radialdirection of the impeller shaft 12 than the outer circumferential edgeof the annular portion 52 b of the second plate 52.

The annular plate 70 includes an outer circumferential edge 71, whichextends between the end face 31 d of the circumferential wall 31 b andthe end face 25 a of the second extended portion 25. The outercircumferential edge 71 of the annular plate 70 is held between the endface 31 d of the circumferential wall 31 b and the end face 25 a of thesecond extended portion 25 by the fastening force of the bolt 17, whichis a fastener. That is, the outer circumferential edge 71 of the annularplate 70 is held between the turbine housing 30 and the bearing housing20.

The annular plate 70 includes a annular rib 73, which protrudes from aninner circumferential portion 72 of the annular plate 70 in the rotationaxis direction of the impeller shaft 12. Specifically, the rib 73extends away from the scroll passage defining plate 60, that is, towardthe bearing housing 20. The rib 73 extends along the outercircumferential edge of the first plate 51.

A small clearance may be provided between the inner circumferentialsurface of the rib 73 and the outer circumferential edge of the firstplate 51. In this case, since the rib 73 does not contact the firstplate 51, thermal expansion of the annular plate 70 is permitted.

The outer circumferential edge 71 of the annular plate 70 may be definedas a fixed end that is held between the bearing housing 20 and theturbine housing 30. Also, the inner circumferential portion 72 and therib 73, which are the remainder of the annular plate 70, may beconfigured not to be fixed to other members. This configuration allowsfor thermal expansion of the annular plate 70.

The turbocharger 10 includes a tubular discharge port defining member80, which constitutes the wall surface of the discharge port 32 a. Thedischarge port defining member 80 is made of a metal sheet. Thedischarge port defining member 80 includes a discharge port main bodywall 81, which constitutes the wall surface of the discharge port 32 a,and an annular discharge port outer circumferential edge 82, whichextends radially outward from an end of the discharge port main bodywall 81. The discharge port main body wall 81 is arranged radiallyinward from the turbine tubular portion 32. The discharge port main bodywall 81 has a proximal end 81 a, which is closer to the turbine chamber33, and a distal end, which is on the opposite side from the proximalend 81 a. The discharge port outer circumferential edge 82 extendsoutward in the radial direction of the impeller shaft 12 from the distalend of the discharge port main body wall 81.

The proximal end 81 a of the discharge port main body wall 81 maysurround the end of the cylindrical portion 52 a of the second plate 52that is on the side opposite from the annular portion 52 b.Specifically, the cylindrical portion 52 a extends toward the dischargeport 32 a along the inner circumferential surface of the turbine tubularportion 32. The distal portion of the cylindrical portion 52 a isarranged inward from the proximal end 81 a of the discharge port mainbody wall 81 in the radial direction of the turbine housing 30. Aclearance may be provided between the proximal end 81 a of the dischargeport main body wall 81 and the cylindrical portion 52 a. If the proximalend 81 a of the discharge port main body wall 81 is spaced apart fromthe turbine housing 30 and the cylindrical portion 52 a, thermalexpansion of the discharge port main body wall 81 is permitted.

A discharge port elastic member 83 is arranged between the dischargeport main body wall 81 and the turbine housing 30, for example, betweenthe proximal end 81 a and the inner circumferential surface of theturbine tubular portion 32. The discharge port elastic member 83, forexample, an annular wire mesh attached to an outer circumferentialsurface 81 b of the discharge port main body wall 81. The elastic member83 may be arranged to be closer to the proximal end 81 a of thedischarge port main body wall 81 than the distal end.

The discharge port elastic member 83 is provided in a crushed statebetween the outer circumferential surface 81 b of the discharge portmain body wall 81 and the inner circumferential surface of the turbinetubular portion 32. The discharge port elastic member 83 is welded tothe outer circumferential surface 81 b of the discharge port main bodywall 81, for example, by micro spot welding. The discharge port mainbody wall 81 is thus supported by the turbine tubular portion 32 withthe discharge port elastic member 83 in between. If the discharge portmain body wall 81 is not fixed using the elastic member 83, the proximalend 81 a of the discharge port main body wall 81 is a free end that isnot fixed to another member.

The discharge port outer circumferential edge 82 protrudes from theopening of the turbine tubular portion 32 and extends along the open endface 32 e of the turbine tubular portion 32. The discharge port outercircumferential edge 82 is held between the open end face 32 e of theturbine tubular portion 32 and the end face 19 e of the downstreamexhaust pipe 19 by the fastening force of the clamp member 19 c. Thatis, the discharge port outer circumferential edge 82 is fixed betweenthe turbine housing 30 and the downstream exhaust pipe 19.

The discharge port defining member 80 may be arranged in the turbinehousing 30 with the proximal end 81 a of the discharge port main bodywall 81 being spaced apart from the inner circumferential surface of theturbine housing 30. The space between the discharge port main body wall81 and the inner circumferential surface of the turbine housing 30allows for thermal expansion of the discharge port defining member 80.This space is a discharge port air layer 84, which is provided betweenthe outer circumferential surface 81 b of the discharge port main bodywall 81 and the inner circumferential surface of the turbine tubularportion 32. The discharge port air layer 84 is a discharge port heatinsulating layer provided between the discharge port defining member 80and the turbine housing 30. In this manner, the discharge port definingmember 80 may be arranged such that a predetermined clearance existsbetween the discharge port defining member 80 and the innercircumferential surface of the turbine housing 30 such that a heatinsulating layer is provided between the discharge port main body wall81 and the turbine housing 30. The heat insulating layer limits thetransfer of heat from the exhaust gas to the turbine housing 30. Theconfiguration thus limits the temperature reduction in the exhaust gasflowing through the turbine scroll passage 35.

As shown in FIG. 3, the turbocharger 10 includes an intake port 37 a,which conducts exhaust gas discharged from the internal combustionengine E to the turbine scroll passage 35. The turbine housing 30 has anintake port defining protrusion 37, which protrudes from the outercircumferential surface of the turbine housing 30. For the illustrativepurposes, the second plate 52 and the turbine impeller 13 are notillustrated in FIG. 3. The intake port 37 a is provided inward from theintake port defining protrusion 37. The intake port 37 a is thusprovided in the turbine housing 30.

The turbocharger 10 includes a tubular intake port defining member 90,which constitutes the wall surface of the intake port 37 a. The intakeport defining member 90 is made of a metal sheet. The intake portdefining member 90 is inserted into the intake port defining protrusion37. The end of the intake port defining member 90 that is closer to theturbine scroll passage 35 is connected to the scroll passage definingplate 60 via a tubular connecting member 91. The inner space of theintake port defining member 90 and the inner space of the scroll passagedefining plate 60 are continuous with each other via the inner space ofthe connecting member 91. Thus, the intake port 37 a and the turbinescroll passage 35 are continuous with each other via the inner space ofthe connecting member 91.

The turbocharger 10 includes an intake port air layer 92, which isprovided between the outer circumferential surface of the intake portdefining member 90 and the inner circumferential surface of the intakeport defining protrusion 37. The intake port air layer 92 is thus anintake port heat insulating layer provided between the intake portdefining member 90 and the turbine housing 30.

An intake port elastic member 93 is arranged between the outercircumferential surface of the intake port defining member 90 and theinner circumferential surface of the intake port defining protrusion 37.The intake port elastic member 93 may be located in a part of the intakeport defining member 90 that is close to the turbine scroll passage 35.

The intake port elastic member 93 is, for example, an annular wire meshattached to the outer circumferential surface of the intake portdefining member 90. Since the wire mesh allows for passage of air,pressure difference is not easily created between the intake port airlayer 92 and the intake port 37 a. This limits deformation of the intakeport defining member 90 caused by the pressure difference.

The intake port elastic member 93 is provided in a crushed state betweenthe outer circumferential surface of the intake port defining member 90and the inner circumferential surface of the intake port definingprotrusion 37. The intake port elastic member 93 is welded to the outercircumferential surface of the intake port defining member 90, forexample, by micro spot welding. The intake port defining member 90 isthus supported by the turbine housing 30 with the intake port elasticmember 93 in between.

The intake port defining member 90 includes an annular intake port outercircumferential edge 90 f, which protrudes from the intake port definingprotrusion 37 and extends along an open end face 37 e of the intake portdefining protrusion 37. The intake port outer circumferential edge 90 fis held between an end face 94 e of an upstream exhaust pipe 94connected to the intake port 37 a and the open end face 37 e of theintake port defining protrusion 37. That is, the intake port outercircumferential edge 90 f is held between the turbine housing 30 and theupstream exhaust pipe 94. The intake port outer circumferential edge 90f is held between the end face 94 e of the upstream exhaust pipe 94 andthe open end face 37 e of the intake port defining protrusion 37 byfastening force of a bolt (not shown) that fastens the upstream exhaustpipe 94 and the intake port defining protrusion 37 together.

The operation of the present embodiment will now be described.

Exhaust gas discharged from the internal combustion engine E isconducted to the turbine scroll passage 35 via the intake port 37 a.When the exhaust gas flows through the intake port 37 a, the intake portdefining member 90 limits the transfer of heat from the exhaust gas tothe turbine housing 30. The intake port air layer 92 limits the transferof heat from the intake port defining member 90 to the turbine housing30.

The exhaust gas conducted to the turbine scroll passage 35 is thenconducted to the turbine chamber 33 via the connecting passage 34. Whenthe exhaust gas flows through the turbine scroll passage 35, the scrollpassage defining plate 60 and the annular plate 70 limit the transfer ofheat from the exhaust gas to the turbine housing 30. The scroll heatinsulator 65 limits the transfer of heat from the scroll passagedefining plate 60 to the turbine housing 30.

When the exhaust gas is drawn into the turbine chamber 33, the turbineimpeller 13 is rotated by receiving the flow of the exhaust gas drawninto the turbine chamber 33. As the turbine impeller 13 rotates, thecompressor impeller 14 is rotated integrally with the turbine impeller13 through the impeller shaft 12. When the compressor impeller 14rotates, the intake air drawn into the compressor impeller chamber 43through the intake port 42 a is compressed by rotation of the compressorimpeller 14. The velocity of the intake air is then reduced when passingthrough the diffuser passage 44. This converts the velocity energy ofthe intake air into pressure energy. The intake air, the pressure ofwhich has been increased, is discharged to the compressor scroll passage45 to be supplied to the internal combustion engine E. Suchforced-induction of the intake air into the internal combustion engine Eis performed by the turbocharger 10 to increase the charging efficiencyof the internal combustion engine E. This improves the performance ofthe internal combustion engine E.

The exhaust gas that has passed through the turbine chamber 33 isconducted to the discharge port 32 a and then flows into the downstreamexhaust pipe 19 via the discharge port 32 a. When the exhaust gas flowsthrough the discharge port 32 a, the discharge port defining member 80limits the transfer of heat from the exhaust gas to the turbine housing30. The discharge port air layer 84 limits the transfer of heat from thedischarge port defining member 80 to the turbine housing 30.

The exhaust gas that has flowed into the downstream exhaust pipe 19 fromthe discharge port 32 a reaches the catalyst C1 after passing throughthe downstream exhaust pipe 19. The intake port defining member 90, thescroll passage defining plate 60, the annular plate 70, and thedischarge port defining member 80 limit the transfer of heat from theexhaust gas to the turbine housing 30. Thus, the heat of the exhaust gasflowing through the turbine housing 30 is not easily removed, so thatthe temperature of the exhaust gas is not easily reduced. This shortensthe time for the catalyst C1 to reach the activation temperature.Therefore, for example, under the operating condition in which there isa demand for early warm-up of the catalyst C1, for example, during coldstart of the internal combustion engine E, the catalyst C1 is readilyheated to a temperature higher than or equal to the activationtemperature at an early stage.

The above described embodiment has the following advantages.

(1) The scroll elastic member 66 is arranged between the turbine housing30 and the end of the outer circumferential surface 61 a of the outercircumferential wall 61 of the scroll passage defining plate 60 that ison the opposite side from the linking wall 63. The outer circumferentialwall 61 of the scroll passage defining plate 60 is thus movable relativeto the turbine housing 30. Elastic deformation of the scroll elasticmember 66 allows for thermal expansion of the scroll passage definingplate 60 caused by heating of the scroll passage defining plate 60 bythe heat of exhaust gas. Also, the outer circumferential wall 61 of thescroll passage defining plate 60 is supported by the turbine housing 30with the scroll elastic member 66, and the inner circumferential edge 64of the scroll passage defining plate 60 is held between the turbinehousing 30 and the second plate 52. This suppresses vibrations of thescroll passage defining plate 60. The present embodiment thus allows forthermal expansion of the scroll passage defining plate 60, whilesuppressing vibrations of the scroll passage defining plate 60.

(2) The flange portion 67 of the scroll passage defining plate 60 limitsentry of exhaust gas flowing through the turbine scroll passage 35 intothe gap between the scroll passage defining plate 60 and the turbinehousing 30 through the gap between the edge of the outer circumferentialwall 61 of the scroll passage defining plate 60 and the turbine housing30. This allows transfer of heat from the exhaust gas flowing throughthe turbine scroll passage 35 to the turbine housing 30 to be easilylimited.

(3) The turbocharger 10 further includes the annular plate 70, which ismade of a metal sheet and constitutes the wall surface of the turbinescroll passage 35 that is closer to the bearing housing 20. In therotation axis direction of the impeller shaft 12, the annular plate 70is arranged to be opposed to the linking wall 63 of the scroll passagedefining plate 60. The thickness of the annular plate 70 is smaller thanthe thicknesses of the first plate 51 and the second plate 52, and theouter circumferential edge 71 of the annular plate 70 is held betweenthe turbine housing 30 and the bearing housing 20. This configurationeffectively limits the reduction in the temperature of the exhaust gasflowing through the turbine scroll passage 35 as compared to acomparative example in which, for example, a part of the first plate 51is arranged, in the rotation axis direction of the impeller shaft 12, tobe opposed to most of the linking wall 63 of the scroll passage definingplate 60, and a part of the first plate 51 constitutes the wall surfaceof the turbine scroll passage 35 that is closer to the bearing housing20.

(4) The annular plate 70 includes the annular rib 73, which protrudesfrom the inner circumferential portion 72 of the annular plate 70 in therotation axis direction of the impeller shaft 12. Specifically, the rib73 protrudes away from the scroll passage defining plate 60. The rib 73increases the stiffness of the annular plate 70. Also, vibrations in asection close to the inner circumferential portion 72 of the annularplate 70 are more suppressed than in a case in which the annular plate70 does not have the rib 73.

(5) The turbocharger 10 further includes the tubular discharge portdefining member 80, which constitutes the wall surface of the dischargeport 32 a. The discharge port defining member 80 is made of a metalsheet. The discharge port defining member 80 limits the transfer of heatfrom exhaust gas to the turbine housing 30. Thus, the temperature of theexhaust gas is prevented from being reduced when flowing through thedischarge port 32 a. Further, the discharge port elastic member 83 isarranged between the turbine housing 30 and the end of the outercircumferential surface 81 b of the discharge port main body wall 81 ofthe discharge port defining member 80 that is closer to the turbinechamber 33. Elastic deformation of the discharge port elastic member 83allows for thermal expansion of the discharge port defining member 80that is caused when the discharge port defining member 80 is warmed bythe heat of the exhaust gas. Also, the discharge port main body wall 81is supported by the turbine housing 30 with the discharge port elasticmember 83, and the discharge port outer circumferential edge 82 of thedischarge port defining member 80 is held between the turbine housing 30and the downstream exhaust pipe 19. This suppresses vibrations of thedischarge port defining member 80. The present embodiment thus allowsfor thermal expansion of the discharge port defining member 80, whilesuppressing vibrations of the discharge port defining member 80.

(6) The turbocharger 10 further includes the tubular intake portdefining member 90, which constitutes the wall surface of the intakeport 37 a. The intake port defining member 90 is made of a metal sheet.The intake port defining member 90 limits the transfer of heat fromexhaust gas to the turbine housing 30. Thus, the temperature of theexhaust gas is prevented from being reduced when flowing through theintake port 37 a.

(7) A part of the wall surface of the turbine scroll passage 35 isconstituted by the scroll passage defining plate 60, which is made of ametal sheet, and the annular plate 70. The wall surface of the dischargeport 32 a is constituted by the discharge port defining member 80, whichis made of a metal sheet. The wall surface of the intake port 37 a isconstituted by the intake port defining member 90, which is made of ametal sheet. This configuration reduces the thermal stress of theturbine housing 30. Accordingly, the reliability and the durability ofthe turbine housing 30 are improved.

(8) A part of the wall surface of the turbine scroll passage 35 isconstituted by the annular plate 70 and the scroll passage definingplate 60, which is made of a metal sheet. This configuration reduces theresistance of the wall surface against the exhaust gas flowing throughthe turbine scroll passage 35 as compared to a configuration in whichthe wall surface of the turbine scroll passage 35 is a casting surfaceof the turbine housing 30.

(9) The wall surface of the discharge port 32 a is constituted by thedischarge port defining member 80, which is made of a metal sheet. Thisconfiguration reduces the resistance of the wall surface against theexhaust gas flowing through the discharge port 32 a as compared to aconfiguration in which the wall surface of the discharge port 32 a is acasting surface of the turbine housing 30.

(10) The wall surface of the intake port 37 a is constituted by theintake port defining member 90, which is made of a metal sheet. Thisconfiguration reduces the resistance of the wall surface against theexhaust gas flowing through the intake port 37 a as compared to aconfiguration in which the wall surface of the intake port 37 a is acasting surface of the turbine housing 30.

(11) The intake port defining member 90, the scroll passage definingplate 60, the annular plate 70, and the discharge port defining member80 limit the transfer of heat from the exhaust gas to the turbinehousing 30. Thus, the heat of the exhaust gas flowing through theturbine housing 30 is not easily removed, so that the temperature of theexhaust gas is not easily reduced. This shortens the time for thecatalyst C1 to reach the activation temperature. Therefore, for example,under the operating condition in which there is a demand for earlywarm-up of the catalyst C1, for example, during cold start of theinternal combustion engine E, the catalyst C1 is heated to a temperaturehigher than or equal to the activation temperature at an early stage.

(12) The intake port elastic member 93 is arranged between a section inthe outer circumferential surface of the intake port defining member 90that is close to the turbine scroll passage 35 and the innercircumferential surface of the intake port defining protrusion 37.Elastic deformation of the intake port elastic member 93 allows forthermal expansion of the intake port defining member 90 that is causedwhen the intake port defining member 90 is warmed by the heat of theexhaust gas. Also, the intake port defining member 90 is supported bythe turbine housing 30 with the intake port elastic member 93, and theintake port outer circumferential edge 90 f of the intake port definingmember 90 is held between the turbine housing 30 and the upstreamexhaust pipe 94. This suppresses vibrations of the intake port definingmember 90. The present embodiment thus allows for thermal expansion ofthe intake port defining member 90, while suppressing vibrations of theintake port defining member 90.

The above-described embodiment may be modified as follows. The featuresincluded in the above-described embodiment and the features included inthe following modifications can be combined as needed. The features inthe following modifications can be combined as needed.

In the above-described embodiment, the turbocharger 10 does notnecessarily need to include the intake port defining member 90. The wallsurface of the intake port 37 a may be constituted by a casting surfaceof the turbine housing 30.

In the above-described embodiment, the turbocharger 10 does notnecessarily need to include the discharge port defining member 80. Thewall surface of the discharge port 32 a may be constituted by a castingsurface of the turbine housing 30.

In the above-described embodiment, the turbocharger 10 does notnecessarily need to include the annular plate 70. For example, a part ofthe first plate 51 may be arranged, in the rotation axis direction ofthe impeller shaft 12, to be opposed to most of the linking wall 63 ofthe scroll passage defining plate 60, and a part of the first plate 51may constitute the wall surface of the turbine scroll passage 35 that iscloser to the bearing housing 20.

In the above-described embodiment, the annular plate 70 does notnecessarily need to include the annular rib 73, which protrudes from theinner circumferential portion 72 and extends away from the linking wall63.

In the above-described embodiment, the scroll passage defining plate 60does not necessarily include the flange portion 67, which extendsoutward in the radial direction of the impeller shaft 12 from the edgeof the outer circumferential wall 61 on the side opposite from thelinking wall 63.

In the above-described embodiment, the turbocharger 10 does notnecessarily need to include the scroll heat insulator 65. For example,the turbocharger 10 may include an air layer that extends over the spacebetween the outer circumferential surface 61 a of the outercircumferential wall 61 and the inner circumferential surface of thecircumferential wall 31 b, the space between the outer circumferentialsurface 61 a of the outer circumferential wall 61 and the innercircumferential surface of the bulging outer circumferential wall 36 a,the space between the outer circumferential surface 63 a of the linkingwall 63, and the space between the outer circumferential surface 62 a ofthe inner circumferential wall 62 and the inner circumferential surfaceof the bulging inner circumferential wall 36 b. In short, theturbocharger 10 simply needs to include a scroll heat insulating layerprovided between the scroll passage defining plate 60 and the turbinehousing 30.

In the above-described embodiment, the turbocharger 10 may include adischarge port heat insulator between the outer circumferential surface81 b of the discharge port main body wall 81 and the innercircumferential surface of the turbine tubular portion 32. In short, theturbocharger 10 simply needs to include a discharge port heat insulatinglayer provided between the discharge port defining member 80 and theturbine housing 30.

In the above-described embodiment, the turbocharger 10 may include anintake port heat insulator between the intake port defining member 90and the turbine housing 30. In short, the turbocharger 10 simply needsto include an intake port heat insulating layer provided between theintake port defining member 90 and the turbine housing 30.

In the above-described embodiment, the scroll passage defining plate 60and the connecting member 91 may be integrated.

The nozzle vanes 50 may be fixed vanes fixed to the first plate 51 orthe second plate 52. For example, as in a first modification illustratedin FIG. 4, fixed vanes may be fixed to the first plate 51. When thenozzle vanes 50 are fixed vanes, one of the plates 51, 52 that does notsupport the fixed vanes, the spacers 53, and the link member 54 may beomitted. Thus, if the nozzle vanes 50 are fixed vanes, the number ofcomponents is reduced. The nozzle vanes 50, that is, fixed vanes andmovable vanes, are arranged in the connecting passage 34 to causeexhaust gas in the turbine scroll passage 35 to flow to the turbinechamber 33.

When fixed vanes are fixed to the second plate 52 as shown in FIG. 4,the flow passage defining portion, which is a part of the annular plate70 that defines the turbine scroll passage 35, may be extended to aposition that is opposed to the metal plate 52 (the second plate 52). Inthis case, the annular plate 70 defines the connecting passage 34. Ifthe connecting passage 34 is defined by the metal annular plate 70, thetransfer of heat from exhaust gas flowing through the connecting passage34 to the bearing housing 20 is limited. Further, the innercircumferential edge of the annular plate 70 may be engaged with theleaf spring 55 so as to support the passage defining portion of theannular plate 70.

As shown in FIGS. 4 and 5, the outer circumferential edge 71 of theannular plate 70 may extend to a position between the end face 31 c ofthe flange 31 f and the end face 26 a of the third extended portion 26of the bearing housing 20, such that the annular plate 70 seals theinterface between the bearing housing 20 and the turbine housing 30. Inthis case, the outer circumferential edge 71 of the annular plate 70functions as a gasket portion that is held between the bearing housing20 and the turbine housing 30 so as to seal the interface between thebearing housing 20 and the turbine housing 30. This eliminates thenecessity for the seal member 18, reducing the number of components. Inthe configuration of FIGS. 1 and 2, the outer circumferential edge 71 ofthe annular plate 70 may be extended such that the annular plate 70seals the interface between the bearing housing 20 and the turbinehousing 30 as shown in FIGS. 4 and 5.

As shown in FIG. 4, the third extended portion 26 of the bearing housing20 may have a positioning projection 26 b, and the annular plate 70 andthe flange 31 f may respectively have positioning through-holes 71 a, 31g for receiving the projection 26 b. This facilitates the assembly ofthe bearing housing 20, the annular plate 70, and the turbine housing30.

In the configuration of FIGS. 1 and 2, the scroll elastic member 66 maybe omitted as shown in FIG. 4, and the outer circumferential wall 61does not necessarily need to be fixed to the turbine housing 30. Forexample, the scroll passage defining plate 60 may be configured suchthat only the inner circumferential edge 64 is fixed to the turbinehousing 30, and the remaining portion (the passage defining portion) isnot fixed to or supported by the turbine housing 30. In this case, theouter circumferential wall 61, particularly the outer circumferentialedge portion of the passage defining portion, is spaced apart from theinner circumferential surface of the turbine housing 30, the distal endof the outer circumferential wall 61 (the end on the side opposite fromthe linking wall 63) is a free end that is not fixed to another member.That is, the scroll passage defining plate 60 is arranged in the turbinehousing 30 such that the inner circumferential edge 64 is fixed betweenthe turbine housing 30 and the metal plate 52, and the outercircumferential edge portion of the passage defining portion is movablerelative to the turbine housing 30. This allows for thermal expansion ofthe scroll passage defining plate 60 due to heating of the scrollpassage defining plate 60 the heat of the exhaust gas.

In the configuration of FIGS. 1 and 2, the discharge port elastic member83 does not necessarily need to be provided between the discharge portdefining member 80 and the turbine housing 30 as shown in FIG. 4.

As shown in FIG. 4, the proximal end 81 a of the discharge port definingmember 80 may be spaced apart from the cylindrical portion 52 a of thesecond plate 52 in the rotation axis direction of the impeller shaft 12.This allows for thermal expansion of the discharge port main body wall81.

As in a second modification illustrated in FIG. 4, when the bearinghousing 20 and the turbine housing 30 are fixed to each other by afastener (the bolt 17), the annular plate 70 may have an insertion hole(a bolt hole 71 b), through which the fastener (the bolt 17) is passed,in addition to the insertion holes (the bolt holes) of the bearinghousing 20 and the turbine housing 30, through which the fastener ispassed. In this case, the bolt 17 may also be passed through the annularplate 70 to fasten the bearing housing 20, the annular plate 70, and theturbine housing 30 together. This properly seal the interface betweenthe bearing housing 20 and the annular plate 70 and the interfacebetween the annular plate 70 and the turbine housing 30.

In the configuration of FIGS. 1 and 2, the annular leaf spring 55 may bearranged between the inner circumferential edge 64 of the scroll passagedefining plate 60 and the end wall 31 a of the turbine housing 30 asillustrated in FIG. 5. When the leaf spring 55 is arranged between theinner circumferential edge 64 and the turbine housing 30, the scrollpassage defining plate 60 is fixed by holding the inner circumferentialedge 64 between the leaf spring 55 and the metal plate 52. This reducesthe contact area between the turbine housing 30 and the scroll passagedefining plate 60. This limits the transfer of heat from the exhaust gasflowing through the turbine scroll passage 35 to the turbine housing 30.

In this case, the inner circumferential edge of the leaf spring 55 maybe brought into contact with the turbine housing 30, and the outercircumferential edge of the leaf spring 55 may be brought into contactwith the scroll passage defining plate 60. Alternatively, the outercircumferential edge of the leaf spring 55 may be brought into contactwith the turbine housing 30, and the inner circumferential edge of theleaf spring 55 may be brought into contact with the scroll passagedefining plate 60. Also, the interface between the protrusion 21 f ofthe bearing housing 20 and the first plate 51 may be sealed by a sealmember 21 j.

As shown in FIG. 5, a clearance may be provided between the proximal end81 a of the discharge port defining member 80 and the turbine housing30, and a clearance may be provided between the proximal end 81 a of thedischarge port defining member 80 and the cylindrical portion 52 a. Thisconnects the discharge port air layer 84 and the discharge port airlayer 84 to each other, so that a pressure difference is unlikely to becaused between the discharge port air layer 84 and the discharge port 32a. This limits deformation of the discharge port defining member 80caused by the pressure difference.

Further, the cylindrical portion 52 a may be arranged inward from theproximal end 81 a of the discharge port main body wall 81, and aclearance may be provided between the proximal end 81 a of the dischargeport main body wall 81 and the cylindrical portion 52 a. This hindersentry of the air flowing from the discharge port 32 a to the turbinescroll passage 35 into the discharge port air layer 84. This limits thetransfer of heat from the exhaust gas to the turbine housing 30.

As shown in FIG. 5, the discharge port defining member 80 may has afold-back portion 82 a, which is a bent portion, between the dischargeport main body wall 81 and the discharge port outer circumferential edge82. This configuration reduces the contact area between the dischargeport outer circumferential edge 82 and the turbine housing 30. As aresult, the transfer of heat from the discharge port defining member 80to the turbine housing 30 is limited.

As shown in FIGS. 6 and 7, the annular plate 70 may include a bead 75arranged between the bearing housing 20 and the turbine housing 30. Inthis case, even if the shape of the annular plate 70 has distortion, thebead 75 is crushed when the bearing housing 20 and the turbine housing30 are fastened together, so that the interface between the bearinghousing 20 and the turbine housing 30 is properly sealed. The bead 75may be a full bead, which protrude in one direction, or a half-bead,which includes a step portion as shown in FIG. 7. The bead in the gasketportion (the outer circumferential edge 71) of the annular plate 70 maybe annular as shown in FIGS. 6 and 7. Alternatively, the bead may beconstituted by protuberances or recesses arranged at predeterminedintervals.

In the configuration of FIG. 3, a scroll heat insulator does notnecessarily need to be provided between the scroll passage definingplate 60 and the turbine housing 30. Instead, a heat insulating layer,which is an air layer 65, may be provided. In this case, a clearance maybe provided between the open end of the scroll passage defining plate 60and the turbine housing 30, such that the clearance connects the turbinescroll passage 35 and the air layer 65 to each other. This configurationis unlikely to cause a pressure difference between the air layer 65 andthe turbine scroll passage 35. This limits deformation of the scrollpassage defining plate 60 caused by the pressure difference.

In the configuration shown in FIG. 3, the connecting member 91 does notnecessarily need to be provided between the intake port defining member90 and the scroll passage defining plate 60. In this case, asillustrated in FIG. 8, an end of the intake port defining member 90 maybe inserted slightly into the opening of the scroll passage definingplate 60. In this configuration, although the air layer 65 and thescroll passage defining plate 60 are connected with each other, air flowthat flows from the intake port 37 a to the turbine scroll passage 35 isunlikely to flow into the air layer 65. This limits the transfer of heatfrom the exhaust gas to the turbine housing 30.

The intake port elastic member 93 shown in FIGS. 3 and 8 may be omitted.

The invention claimed is:
 1. A turbocharger comprising: a bearinghousing that rotationally supports an impeller shaft; a turbine housingthat is a cast component coupled to an end of the bearing housing in arotation axis direction of the impeller shaft, wherein exhaust gasdischarged from an internal combustion engine flows inside the turbinehousing; a turbine chamber defined in the turbine housing; a turbineimpeller that is accommodated in the turbine chamber and is configuredto be rotated integrally with the impeller shaft by exhaust gas drawninto the turbine chamber; a turbine scroll passage that is defined inthe turbine housing and is a part of a passage for conducting exhaustgas that has flowed into the turbine housing to the turbine chamber, theturbine scroll passage surrounding a circumference of the turbinechamber; a connecting passage that is defined in the turbine housing andconnects the turbine scroll passage and the turbine chamber to eachother; an annular metal plate that constitutes a part of a wall surfaceof the connecting passage; and a scroll passage defining plate thatincludes a passage defining portion that is arranged such that apredetermined clearance is provided between the passage defining portionand the turbine housing, the passage defining portion constituting apart of a wall surface of the turbine scroll passage, and an innercircumferential edge that extends from an inner circumferential edgeportion of the passage defining portion and along the metal plate,wherein the scroll passage defining plate is arranged in the turbinehousing such that the inner circumferential edge is fixed between theturbine housing and the metal plate, and an outer circumferential edgeportion of the passage defining portion that is on a side opposite fromthe inner circumferential edge portion is movable relative to theturbine housing.
 2. The turbocharger according to claim 1, wherein thescroll passage defining plate is arranged in the turbine housing suchthat the outer circumferential edge portion of the passage definingportion and an inner circumferential surface of the turbine housing arespaced apart from each other.
 3. The turbocharger according to claim 1,further comprising an elastic member configured to provide a clearancebetween the passage defining portion of the scroll passage definingplate and the turbine housing.
 4. The turbocharger according to claim 3,wherein the elastic member is arranged between the outer circumferentialedge portion of the passage defining portion and the turbine housing,and the outer circumferential edge portion of the passage definingportion is supported by the turbine housing with the elastic member inbetween.
 5. The turbocharger according to claim 1, further comprising anannular leaf spring that is arranged between the inner circumferentialedge of the scroll passage defining plate and the turbine housing,wherein the scroll passage defining plate is fixed by holding the innercircumferential edge between the leaf spring and the metal plate.
 6. Theturbocharger according to claim 1, wherein the scroll passage definingplate is fixed by holding the inner circumferential edge between theturbine housing and the metal plate.
 7. The turbocharger according toclaim 1, wherein the scroll passage defining plate includes an outercircumferential wall that constitutes an outer circumferential interiorsurface of the turbine scroll passage, an inner circumferential wallthat is located inward from the outer circumferential wall in a radialdirection of the impeller shaft and constitute an inner circumferentialinterior surface of the turbine scroll passage, and a linking wall thatlinks the outer circumferential wall and the inner circumferential wallto each other, wherein the inner circumferential edge of the scrollpassage defining plate extends from the inner circumferential wall andinward in the radial direction of the impeller shaft.
 8. Theturbocharger according to claim 1, wherein a heat insulator is arrangedin the clearance between the passage defining portion of the scrollpassage defining plate and the turbine housing.
 9. The turbochargeraccording to claim 1, further comprising a plurality of nozzle vanesthat is arranged in the connecting passage and causes exhaust gas in theturbine scroll passage to flow to the turbine chamber, wherein the metalplate supports the nozzle vanes.
 10. The turbocharger according to claim9, wherein the nozzle vanes are movable vanes that are pivotallysupported by the metal plate so as to be capable of changing a flowpassage area of the connecting passage, the turbocharger furthercomprises a metal support plate, and the support plate cooperates withthe metal plate to pivotally support the nozzle vanes and is arranged tobe opposed to the metal plate so as to constitute a part of the wallsurface of the connecting passage.
 11. The turbocharger according toclaim 10, further comprising a metal annular plate, wherein the annularplate is arranged to be opposed to the scroll passage defining plate soas to constitute a part of the wall surface of the turbine scrollpassage, a thickness of the annular plate is smaller than a thickness ofthe support plate, and a thickness of the metal plate, and an outercircumferential edge of the annular plate is held between the turbinehousing and the bearing housing.
 12. The turbocharger according to claim1, further comprising a metal annular plate, wherein the annular plateis arranged to be opposed to the scroll passage defining plate so as toconstitute a part of the wall surface of the turbine scroll passage, andan outer circumferential edge of the annular plate is held between theturbine housing and the bearing housing.
 13. The turbocharger accordingto claim 12, wherein the annular plate includes a annular rib, and therib protrudes from an inner circumferential portion of the annular platein the rotation axis direction of the impeller shaft and extends awayfrom the scroll passage defining plate.
 14. The turbocharger accordingto claim 12, wherein the scroll passage defining plate includes a flangeportion that extends from the outer circumferential edge portion of thepassage defining portion and outward in the radial direction of theimpeller shaft, a clearance is provided between the flange portion andthe annular plate, and the flange portion extends along the annularplate.
 15. The turbocharger according to claim 14, wherein the flangeportion extends outward in the radial direction of the impeller shaftsuch that a clearance is provided between the flange portion of thescroll passage defining plate and the inner circumferential surface ofthe turbine housing.